Virtually all fluid handling industrial processes rely on valves and valve assemblies to regulate the inputs, outputs, and rates-of-flow of process ingredients. In some of these processes, extreme cleanliness is imperative to avoid contamination and meet quality requirements, standards and specifications. In certain industries, such as pharmaceutical, food, beverage, semi-conductor and others, such cleanliness is especially important. Commonly, the required cleanliness is maintained by periodic cleaning of process equipment and components (usually between batches).
In some valve designs, chambers or pockets are difficult to access, thereby making it difficult to clean the valves without disassembling the valve components. Such disassembly requirement of the valve increases the process “down-time”. Disassembly may also result in damage to the valve components and valve assembly. One such example is a valve commonly used in the process vessels, such as glass-lined vessels. The bottom of such vessels are typically made with a cylindrical pipe or tube penetrating the vessel bottom and welded thereto. At the bottom of the pipe is a flare/flange that allows connection of other fluid handling components. The fluid contacting surfaces of this pipe and flare/flange are also glass-lined or coated. However, the glass lining is often uneven due to manufacturing limitations. This unevenness prevents the fluid-tight coupling of hard metal valve components with the glass lined nozzle. That is, the uneven glass surface leads to leaks, but tightening a hard metal valve to the nozzle (to stop leaks) leads to glass damage. Thus, to facilitate valve-to-nozzle coupling, valve seats are typically made of a relatively more flexible and soft (compared to glass) plastic material such as PTFE (polytetrafluoroethylene).
A flanged valve mechanism is typically utilized to control the fluid flow through a flanged nozzle. The valve mechanism includes a slightly smaller interior cylindrical member (the seat) that projects up from the bottom into the flared/flanged pipe, and which has a flange pressing against the glass-coated flare/flange surface (to prevent leakage at the bottom connection). The upper inside surface of this seat receives a glass-coated plunger that is attached to a glass coated valve stem projecting downward through the seat. The valve mechanism outside the vessel draws the plunger down into the seat, closing the valve. In reverse, the mechanism pushes the plunger up into the vessel, allowing process fluid to pass around the plunger, into and through the seat, and then on to connected piping. A soft PTFE valve seat allows effective sealing of the various valve components: the glass-coated plunger to the seat, the seat's flange top surface to the glass-coated nozzle flare/flange, and the seat's flange bottom surface to the valve's flange.
The use of known valve seats is illustrated in FIGS. 1 and 2. FIG. 1 is a cross-section view which schematically shows the orientation of a valve seat (1) within a glass lined nozzle (4) of a containment vessel. The cylindrical portion (2) of the valve seat resides within the nozzle (4), while the flange portion (3) of the valve seat (1) resides outside of the nozzle (4) and maintains the position of the valve seat (1) within the nozzle (4). FIG. 2 is a close up depiction of a portion of the valve seat (1) in close contact with the nozzle wall. As seen in FIG. 2, the nozzle wall includes a structural portion (6) typically made of metal, and a glass lined portion (7) having an uneven, irregular surface.
While effectively addressing the need for coupling glass lined vessels and valve assemblies, valve seats currently in use are also a major source of potential impurities and contaminants from the reaction residues. Referring again to FIGS. 1 and 2, it is noted that gaps or interstices (5) are formed between the cylindrical portion (2) of the valve seat and the glass lined portion (7) of the nozzle. In such valve seats, process residues (19) collect in gaps/interstices between the outside surface of the valve seat and the glass-lined inner, irregular surface of the nozzle. In certain chemical processes these residues may represent acceptable amounts of impurities. However, in the pharmaceutical industry, for example, such residues can represent serious contaminants.
The above-described problem of contaminants and impurities is exacerbated when the valve seat is used in connection with high temperature liquids. A PTFE valve seat exposed to high temperature liquids will generally attempt to expand, but will be prevented by the rigid glass lined nozzle. The PTFE material may then “set” in its constrained position, and later shrink when cooled. This shrinkage will result in a decreased outer diameter of the valve seat, and thus a larger gap in which potential contaminants can reside.
To prevent the accumulation of contaminants, the pharmaceutical manufacturer must remove the valve seat and manually remove the residues, often after every batch is processed. This cleaning is both expensive and time consuming, results in process down time, and risks damage to the valve seat and the glass it contacts—all factors which contribute to the overall cost of the manufacturing process.
Several approaches have been tried in attempts to address the contamination problem while minimizing the need to clean, and thus take off line, the valve components. For instance, one manufacturer has developed an inflatable valve seat wherein the inflated outer PTFE skin of the valve fills the space between the valve seat and the uneven surface of the glass-lined vessel's outlet nozzle. Such a valve seat device, however, has several disadvantages. First, any inflated component is susceptible to deflation, and thus failure in its intended purpose, as a result of puncture, excessive or extended wear and tear, leakage or any other reason for which inflated components are known to deflate. Further, an inflated component tends to have rounded surfaces, and thus contact between an inflated surface and rigid glass lining at certain points may be less than snug (e.g., where the curved inflated surface curves away from the irregular but substantially flat glass surface), possibly leading to the presence of crevices where contaminating residues can accumulate. Finally, component inflation adds to the expense necessitating an equipment to inflate and maintain proper inflation levels.
Several manufacturers, for example Xomox Corp. of Cincinnati, Ohio, employ “blade” or “windshield wiper” arrangements to form a seal or seals between the cylindrical valve seat portion and the glass lined nozzle. While this approach reduces the presence of contaminating residues to a degree, the use of a blade type seals is often costly, and more importantly, is less than effective in forming tight and lasting seals to prevent residue accumulation. For example, the arrangement described in Xomox's European patent application EP 0 863 338 A1 employs thin upper and lower blades which are pressed against the nozzle wall with the upper blade oriented in an upward angle and the lower blade oriented at a downward angle. Since there is no structural support for these thin blades and a very tight fit between nozzle and seat, it is likely that during installation one or both blades will not deploy properly (i.e., blades will be folded, creased, oriented at an unintended angle), leading to imperfect seals and accumulation of undesirable residues.
Other non-valve seat devices are similarly disadvantaged, for instance a nozzle repair seat which is the subject of U.S. Pat. No. 5,599,600, owned by Edlon, Inc. of Avondale, Pa. In this device, multiple blades (called “lips” in the patent) are meant to form seals with a vessel's glass lined nozzle surface to prevent contact between a damaged portion of the nozzle and the contents of the vessel. While O-rings are present between blades in certain embodiments of this device, it is clear that the blades, which extent well beyond the O-rings, are equally susceptible to deformations and disorientations during the installation process which will likely lead to the formation of improper seals.